My non-expert opinion is that she is all yorkie. I get Nikko shaved down for the summer and sometimes my groomer gets a little "clipper-happy" and Nikko looks just like this. Except his ears are floppy.
She is a cute girl and I feel sorry for her, but as others have mentioned, the concern is not so much whether she's a purebreed or not, but rather, why does the owner want to get rid of her so soon after just getting her? I would be wary of this ad.